Technical Field
This disclosure relates to a confocal measurement device.
Description of Related Art
In the related art, a confocal measurement device using a confocal optical system has been used as a device that measures displacement of a measurement object in a noncontact manner.
For example, a confocal measurement device described in Patent Document 1 (U.S. Pat. No. 5,785,651) includes a confocal optical system using a diffraction lens between a light source and a measurement object. In such a confocal measurement device, light emitted from the light source is applied to a measurement object with a focal distance based on a wavelength thereof by the confocal optical system. Displacement of the measurement object can be measured by detecting a wavelength peak of reflected light.
A confocal measurement device includes an optical coupler that connects a light source, a sensor head, and a spectroscope using optical fiber cables. For example, Patent Document 2 (Japanese Laid-open No. 2016-024086) discloses a distance measuring device that includes a multiplexing/demultiplexing unit that demultiplexes or multiplexes light incident from a single-mode optical fiber cable.
In some cases, a confocal measurement device guides light emitted from a white light source using an optical fiber cable, generates a chromatic aberration in the light using a diffraction lens or the like, and applies the light to a measurement object. Then, a position of the measurement object can be measured by collecting light reflected by the measurement object in an optical fiber cable, inputting the reflected light to a spectroscope via an optical coupler, and detecting a wavelength peak using the spectroscope. Here, a wavelength of light focused on the optical fiber cable from the light reflected by the measurement object appears as a peak in the spectroscope, and the position of the measurement object can be detected with high accuracy.
When it is intended to detect a position of a measurement object with higher accuracy, it is conceivable that a core diameter of an optical fiber cable corresponding to a pinhole may be further decreased and the wavelength peak detected by the spectroscope may be further sharpened. The inventor of this disclosure or the like manufactured a confocal measurement device for a trial with a core diameter of an optical fiber cable decreased in comparison with that in the related art, and found that transmission characteristics were not good with an optical coupler which has been used in the related art, a wavelength peak was not easily detected by the spectroscope, and a position of a measurement object could not be detected with satisfactory accuracy.